Mine does the clunk too!!! I thought I had it fixed when I corrected a flareing issue, which quickly re-materliazed unless the trans if FULLY warmed up!!

The more I drive the car, the more I'm convinced here is whats happening,

First is WAY SHORT, second you can feel it bump into and then it CLUNKS which I believe is third ,,,,, it revs 3200 rpm at 70mph

planning on doing motor and trans MOUNTS soon, I'm in the process of rebuilding shredded engine "shock mounts"

I'm going to go read your post about transmission fixed!!

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-SpecialDelivery
1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)